U.S. patent number 9,721,605 [Application Number 14/978,834] was granted by the patent office on 2017-08-01 for magnetic tape and method of manufacturing the same.
This patent grant is currently assigned to FUJIFILM Corporation. The grantee listed for this patent is FUJIFILM Corporation. Invention is credited to Norihito Kasada, Kazuyuki Kitada, Masahito Oyanagi, Toshio Tada.
United States Patent |
9,721,605 |
Oyanagi , et al. |
August 1, 2017 |
Magnetic tape and method of manufacturing the same
Abstract
Provided is a magnetic tape, which comprises, on a nonmagnetic
support, a nonmagnetic layer comprising nonmagnetic powder and
binder, and on the nonmagnetic layer, a magnetic layer comprising
ferromagnetic powder and binder; wherein at least the magnetic
layer comprises one or more components selected from the group
consisting of a fatty acid and a fatty acid amide; a quantity of
components selected from the group consisting of a fatty acid and a
fatty acid amide per unit area of the magnetic tape among
components that are extracted from a surface on the magnetic layer
side of the magnetic tape is less than or equal to 15.0 mg/m.sup.2,
and a concentration of carbon, C, that is obtained by X-ray
photoelectron spectroscopy conducted at a photoelectron take-off
angle of 10 degrees on the surface on the magnetic layer side of
the magnetic tape is greater than or equal to 50 atom %.
Inventors: |
Oyanagi; Masahito
(Minami-ashigara, JP), Kasada; Norihito
(Minami-ashigara, JP), Tada; Toshio (Minami-ashigara,
JP), Kitada; Kazuyuki (Minami-ashigara,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
N/A |
JP |
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|
Assignee: |
FUJIFILM Corporation (Tokyo,
JP)
|
Family
ID: |
56164973 |
Appl.
No.: |
14/978,834 |
Filed: |
December 22, 2015 |
Prior Publication Data
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Document
Identifier |
Publication Date |
|
US 20160189740 A1 |
Jun 30, 2016 |
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Foreign Application Priority Data
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Dec 26, 2014 [JP] |
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2014-265723 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B
5/8404 (20130101); G11B 5/71 (20130101); G11B
5/7334 (20190501); G11B 5/733 (20130101); G11B
5/70 (20130101); G11B 5/842 (20130101); G11B
5/78 (20130101) |
Current International
Class: |
G11B
5/71 (20060101); G11B 5/70 (20060101); G11B
5/842 (20060101); G11B 5/73 (20060101); G11B
5/84 (20060101); G11B 5/78 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2002-367142 |
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Dec 2002 |
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JP |
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2008-243317 |
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Oct 2008 |
|
JP |
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Other References
Office Action dated Dec. 6, 2016 in copending U.S. Appl. No.
14/757,555. cited by applicant .
Notice of Allowance dated May 8, 2017 from the U.S. Patent &
Trademark Office in co-pending U.S. Appl. No. 14/757,555. cited by
applicant.
|
Primary Examiner: Bernatz; Kevin
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A magnetic tape, which comprises, on a nonmagnetic support, a
nonmagnetic layer comprising nonmagnetic powder and binder, and on
the nonmagnetic layer, a magnetic layer comprising ferromagnetic
powder and binder; wherein at least the magnetic layer comprises
one or more components selected from the group consisting of a
fatty acid and a fatty acid amide; a quantity of components
selected from the group consisting of a fatty acid and a fatty acid
amide per unit area of the magnetic tape among components that are
extracted from a surface on the magnetic layer side of the magnetic
tape is less than or equal to 15.0 mg/m.sup.2, the extraction being
conducted by immersion of a 5 cm sample of the magnetic tape with
heating in 30 mL of methanol for 3 hours at 60.degree. C.; and a
concentration of carbon, C, that is obtained by X-ray photoelectron
spectroscopy conducted at a photoelectron take-off angle of 10
degrees on the surface on the magnetic layer side of the magnetic
tape is greater than or equal to 50 atom %.
2. The magnetic tape according to claim 1, wherein the
concentration of carbon, C, that is obtained by X-ray photoelectron
spectroscopy conducted at a photoelectron take-off angle of 10
degrees on the surface on the magnetic layer side of the magnetic
tape ranges from 50 atom % to 80 atom %.
3. The magnetic tape according to claim 1, wherein a concentration
of carbon, C, that is obtained by X-ray photoelectron spectroscopy
conducted at a photoelectron take-off angle of 90 degrees on the
surface on the magnetic layer side of the magnetic tape is greater
than or equal to 30 atom % but less than 50 atom %.
4. The magnetic tape according to claim 1, wherein the
concentration of carbon, C, that is obtained by X-ray photoelectron
spectroscopy conducted at a photoelectron take-off angle of 10
degrees on the surface on the magnetic layer side of the magnetic
tape ranges from 50 atom % to 80 atom %, and a concentration of
carbon, C, that is obtained by X-ray photoelectron spectroscopy
conducted at a photoelectron take-off angle of 90 degrees on the
surface on the magnetic layer side of the magnetic tape is greater
than or equal to 30 atom % but less than 50 atom %.
5. The magnetic tape according to claim 1, wherein the quantity of
components selected from the group consisting of a fatty acid and a
fatty acid amide per unit area of the magnetic tape among
components that are extracted from a surface on the magnetic layer
side of the magnetic tape is less than or equal to 12.0
mg/m.sup.2.
6. The magnetic tape according to claim 1, wherein the
concentration of carbon, C, that is obtained by X-ray photoelectron
spectroscopy conducted at a photoelectron take-off angle of 10
degrees on the surface on the magnetic layer side of the magnetic
tape ranges from 50 atom % to 80 atom %, a concentration of carbon,
C, that is obtained by X-ray photoelectron spectroscopy conducted
at a photoelectron take-off angle of 90 degrees on the surface on
the magnetic layer side of the magnetic tape is greater than or
equal to 30 atom % but less than 50 atom %, and the quantity of
components selected from the group consisting of a fatty acid and a
fatty acid amide per unit area of the magnetic tape among
components that are extracted from a surface on the magnetic layer
side of the magnetic tape is less than or equal to 12.0
mg/m.sup.2.
7. The magnetic tape according to claim 1, wherein a thickness of
the nonmagnetic layer ranges from 0.05 .mu.m to 0.60 .mu.m.
8. The magnetic tape according to claim 1, wherein the
concentration of carbon, C, that is obtained by X-ray photoelectron
spectroscopy conducted at a photoelectron take-off angle of 10
degrees on the surface on the magnetic layer side of the magnetic
tape ranges from 50 atom % to 80 atom %, a concentration of carbon,
C, that is obtained by X-ray photoelectron spectroscopy conducted
at a photoelectron take-off angle of 90 degrees on the surface on
the magnetic layer side of the magnetic tape is greater than or
equal to 30 atom % but less than 50 atom %, the quantity of
components selected from the group consisting of a fatty acid and a
fatty acid amide per unit area of the magnetic tape among
components that are extracted from a surface on the magnetic layer
side of the magnetic tape is less than or equal to 12.0 mg/m.sup.2,
and a thickness of the nonmagnetic layer ranges from 0.05 .mu.m to
0.60 .mu.m.
9. The magnetic tape according to claim 1, wherein a centerline
average surface roughness Ra that is measured by a noncontact
surface profiler on the surface on the magnetic layer side of the
magnetic tape is less than or equal to 1.8 nm.
10. The magnetic tape according to claim 1, wherein one or both the
magnetic layer and the nonmagnetic layer further comprise a fatty
acid ester.
11. The magnetic tape according to claim 1, wherein the
ferromagnetic powder is selected from the group consisting of
ferromagnetic hexagonal ferrite powder and ferromagnetic metal
powder.
12. The magnetic tape according to claim 1, wherein the quantity of
components selected from the group consisting of a fatty acid and a
fatty acid amide per unit area of the magnetic tape among
components that are extracted from a surface on the magnetic layer
side of the magnetic tape is within a range of from 9.0 mg/m.sup.2
to 14.7 mg/m.sup.2, and the concentration of carbon, C, that is
obtained by X-ray photoelectron spectroscopy conducted at a
photoelectron take-off angle of 10 degrees on the surface on the
magnetic layer side of the magnetic tape is within the range of
from 50 atom % to 83 atom %.
13. A method of manufacturing a magnetic tape, wherein the magnetic
tape is a magnetic tape, which comprises, on a nonmagnetic support,
a nonmagnetic layer comprising nonmagnetic powder and binder, and
on the nonmagnetic layer, a magnetic layer comprising ferromagnetic
powder and binder; wherein at least the magnetic layer comprises
one or more components selected from the group consisting of a
fatty acid and a fatty acid amide; a quantity of components
selected from the group consisting of a fatty acid and a fatty acid
amide per unit area of the magnetic tape among components that are
extracted from a surface on the magnetic layer side of the magnetic
tape is less than or equal to 15.0 mg/m.sup.2, the extraction being
conducted by immersion of a 5 cm sample of the magnetic tape with
heating in 30 mL of methanol for 3 hours at 60.degree. C., and a
concentration of carbon, C, that is obtained by X-ray photoelectron
spectroscopy conducted at a photoelectron take-off angle of 10
degrees on the surface on the magnetic layer side of the magnetic
tape is greater than or equal to 50 atom %, and the method
comprises a step of forming a nonmagnetic layer and a step of
forming a magnetic layer, wherein the step of forming the
nonmagnetic layer comprises: a coating step of forming a coating
layer by coating on a nonmagnetic support a nonmagnetic layer
forming composition comprising one or more components selected from
the group consisting of a fatty acid and a fatty acid amide,
nonmagnetic powder, binder, and solvent; a heating and drying step
of drying the coating layer by a heat treatment; and the step of
forming the nonmagnetic layer further comprises, between the
coating step and the heating and drying step, a cooling step of
cooling the coating layer.
14. The method of manufacturing a magnetic tape according to claim
13, wherein the cooling step is conducted by placing the coating
layer in a cooling atmosphere of -10.degree. C. to 0.degree. C.
15. The method of manufacturing a magnetic tape according to claim
13, wherein the nonmagnetic layer forming composition comprises
ketone solvent.
16. The method of manufacturing a magnetic tape according to claim
13, wherein the magnetic layer forming step comprises: a coating
step of forming a coating layer by coating on a nonmagnetic layer a
magnetic layer forming composition comprising ferromagnetic powder,
binder, and solvent; and a heating and drying step of drying the
coating layer by a heat treatment.
17. The method of manufacturing a magnetic tape according to claim
16, wherein the magnetic layer forming composition further
comprises one or more components selected from the group consisting
of a fatty acid and a fatty acid amide.
18. The method of manufacturing a magnetic tape according to claim
16, wherein one or both the nonmagnetic layer forming composition
and the magnetic layer forming composition further comprises a
fatty acid ester.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority under 35 U.S.C 119 to Japanese
Patent Application No. 2014-265723 filed on Dec. 26, 2014. The
above application is hereby expressly incorporated by reference, in
its entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a magnetic tape and method of
manufacturing the same.
Discussion of the Background
Magnetic recording media include tape-shaped media and disk-shaped
media. Magnetic recording media in the form of tapes, that is,
magnetic tapes, are primarily employed in storage applications such
as data-backup tapes. To record and reproduce signals on a magnetic
tape, the magnetic tape is normally run within a drive and the
surface on the magnetic layer side of the magnetic tape and a
magnetic head (also simply referred to as a "head", hereinafter)
are brought into contact and slide.
In the above recording and reproduction, when running is repeated
in a state of a high coefficient of friction during sliding of the
head over the surface on the magnetic layer side, the surface on
the magnetic layer side is shaved and scratches (rub marks) end up
being made. These rub marks may cause a drop in electromagnetic
characteristics, so their reduction is desirable. Accordingly, to
prevent the generation of rub marks during repeat running, a
lubricant has conventionally been coated (known as an overcoat) on
the surface of the magnetic layer side of the magnetic tape, or the
magnetic tape has conventionally been fabricated with a composition
containing a lubricant (for example, see Japanese Unexamined Patent
Publication (KOKAI) No. 2008-243317, which is expressly
incorporated herein by reference in its entirety).
SUMMARY OF THE INVENTION
The use of a lubricant as set forth above is an effective way to
prevent the generation of rub marks (enhance the resistance to
scratching) on the surface on the magnetic layer side of a magnetic
tape.
However, based on investigation by the present inventors, in
magnetic tapes in which a lubricant is employed to enhance the
resistance to scratching, signal reading failure known as "dropout"
tends to occur. This dropout increases the error rate, and thus
reduction of the dropout is required.
An aspect of the present invention provides for a magnetic tape
with good resistance to scratching and in which the occurrence of
dropout can be inhibited.
An aspect of the present invention provides a magnetic tape, which
comprises, on a nonmagnetic support, a nonmagnetic layer comprising
nonmagnetic powder and binder, and on the nonmagnetic layer, a
magnetic layer comprising ferromagnetic powder and binder;
wherein at least the magnetic layer comprises one or more
components selected from the group consisting of a fatty acid and a
fatty acid amide;
a quantity of components selected from the group consisting of a
fatty acid and a fatty acid amide per unit area of the magnetic
tape among components that are extracted from a surface on the
magnetic layer side of the magnetic tape (also referred to
hereinafter as the "quantity of magnetic layer side surface
extraction components") is less than or equal to 15.0 mg/m.sup.2,
and
a concentration of carbon, C, that is obtained by X-ray
photoelectron spectroscopy conducted at a photoelectron take-off
angle of 10 degrees on the surface on the magnetic layer side of
the magnetic tape (also referred to hereinafter as the "C
concentration (10 degrees)") is greater than or equal to 50 atom
%.
The above magnetic tape can exhibit good resistance to scratching
and permit reading with low signal dropout. The presumptions of the
present inventors in this regard will be given further below.
In one embodiment, the C concentration (10 degrees) falls within a
range of 50 atom % to 80 atom %.
In one embodiment, the concentration of carbon, C, obtained by
X-ray photoelectron spectroscopy conducted at a photoelectron
take-off angle of 90 degrees on the surface on the magnetic layer
side of the magnetic tape (also referred hereinafter as the "C
concentration (90 degrees)" falls within a range of greater than or
equal to 30 atom % but less than 50 atom %.
In one embodiment, the quantity of the above components per unit
area among the components extracted from the surface on the
magnetic layer side of the magnetic tape is less than or equal to
12.0 mg/m.sup.2.
In one embodiment, the thickness of the nonmagnetic layer falls
within a range of 0.05 .mu.m to 0.60 .mu.m.
In one embodiment, the centerline average surface roughness Ra that
is measured by a noncontact surface profiler on the surface on the
magnetic layer side of the magnetic tape is less than or equal to
1.8 nm.
In one embodiment, one or both the magnetic layer and the
nonmagnetic layer further comprise a fatty acid ester.
In one embodiment, the ferromagnetic powder is selected from the
group consisting of ferromagnetic hexagonal ferrite powder and
ferromagnetic metal powder.
A further aspect of the present invention relates to a method of
manufacturing the above magnetic tape, which comprises a step of
forming a nonmagnetic layer and a step of forming a magnetic layer,
wherein the step of forming the nonmagnetic layer comprises:
a coating step of forming a coating layer by coating on a
nonmagnetic support a nonmagnetic layer forming composition
comprising one or more components selected from the group
consisting of a fatty acid and a fatty acid amide, nonmagnetic
powder, binder, and solvent;
a heating and drying step of drying the coating layer by a heat
treatment; and
the step of forming the nonmagnetic layer further comprises,
between the coating step and the heating and drying step, a cooling
step of cooling the coating layer.
In one embodiment, the cooling step is conducted by placing the
coating layer in a cooling atmosphere of -10.degree. C. to
0.degree. C.
In one embodiment, the solvent contained in the nonmagnetic layer
forming composition contains ketone solvent.
In one embodiment, the magnetic layer forming step comprises:
a coating step of forming a coating layer by coating on a
nonmagnetic layer the magnetic layer forming composition containing
ferromagnetic powder, binder, and solvent; and
a heating and drying step of drying the coating layer by a heat
treatment.
In one embodiment, the magnetic layer forming composition further
comprises one or more components selected from the group consisting
of a fatty acid and a fatty acid amide.
In one embodiment, one or both the nonmagnetic layer forming
composition and the magnetic layer forming composition further
comprises a fatty acid ester.
An aspect of the present invention can provide a magnetic tape that
generates few scratches with repeat running and generates little
dropout during signal reading (reproduction).
Other exemplary embodiments and advantages of the present invention
may be ascertained by reviewing the present disclosure and the
accompanying drawing(s).
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described in the following text by
the exemplary, non-limiting embodiments shown in the drawing,
wherein:
FIG. 1 shows an example (a schematic process diagram) of a specific
embodiment of the process of manufacturing a magnetic tape.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Unless otherwise stated, a reference to a compound or component
includes the compound or component by itself, as well as in
combination with other compounds or components, such as mixtures of
compounds.
As used herein, the singular forms "a," "an," and "the" include the
plural reference unless the context clearly dictates otherwise.
Except where otherwise indicated, all numbers expressing quantities
of ingredients, reaction conditions, and so forth used in the
specification and claims are to be understood as being modified in
all instances by the term "about." Accordingly, unless indicated to
the contrary, the numerical parameters set forth in the following
specification and attached claims are approximations that may vary
depending upon the desired properties sought to be obtained by the
present invention. At the very least, and not to be considered as
an attempt to limit the application of the doctrine of equivalents
to the scope of the claims, each numerical parameter should be
construed in light of the number of significant digits and ordinary
rounding conventions.
Additionally, the recitation of numerical ranges within this
specification is considered to be a disclosure of all numerical
values and ranges within that range. For example, if a range is
from about 1 to about 50, it is deemed to include, for example, 1,
7, 34, 46.1, 23.7, or any other value or range within the
range.
The following preferred specific embodiments are, therefore, to be
construed as merely illustrative, and non-limiting to the remainder
of the disclosure in any way whatsoever. In this regard, no attempt
is made to show structural details of the present invention in more
detail than is necessary for fundamental understanding of the
present invention; the description taken with the drawings making
apparent to those skilled in the art how several forms of the
present invention may be embodied in practice.
The magnetic tape according to an aspect of the present invention
is a magnetic tape, which comprises, on a nonmagnetic support, a
nonmagnetic layer comprising nonmagnetic powder and binder, and on
the nonmagnetic layer, a magnetic layer comprising ferromagnetic
powder and binder; wherein at least the magnetic layer comprises
one or more components selected from the group consisting of a
fatty acid and a fatty acid amide; a quantity of components
selected from the group consisting of a fatty acid and a fatty acid
amide per unit area of the magnetic tape among components that are
extracted from a surface on the magnetic layer side of the magnetic
tape (quantity of magnetic layer side surface extraction
components) is less than or equal to 15.0 mg/m.sup.2, and a
concentration of carbon, C, that is obtained by X-ray photoelectron
spectroscopy conducted at a photoelectron take-off angle of 10
degrees on the surface on the magnetic layer side of the magnetic
tape (C concentration (10 degrees)) is greater than or equal to 50
atom %.
In the above magnetic tape, one or more components selected from
the group consisting of a fatty acid and a fatty acid amide are
contained in at least the magnetic layer. The present inventors
assume that both the fatty acid and the fatty acid amide can
function as lubricants in the magnetic tape and can contribute to
enhancing the resistance to scratching of the magnetic tape.
However, the present inventors presume that these components may be
factors in the generation of dropout set forth above. They assume
that these components soften the magnetic layer or nonmagnetic
layer, and thus transfer of the roughness of the surface on the
opposite side (the surface of the nonmagnetic support or the
surface of the backcoat layer, described further below) to the
surface of the magnetic layer side of the magnetic tape, what is
known as back surface transfer, resulting in facilitating the
occurrence of dropout.
Accordingly, when the content of the one or more components
selected from the group consisting of a fatty acid and a fatty acid
amide in the magnetic tape was reduced to where the magnetic layer
side surface extraction quantity was less than or equal to 15.0
mg/m.sup.2, it became possible to inhibit the generation of
dropout. However, just reducing the quantity of this component to
inhibit the generation of dropout presented a tradeoff where the
resistance to scratching also ended up decreasing. It was still
just as difficult to achieve both enhanced resistance to scratching
and decreased dropout.
Accordingly, the present inventors conducted further extensive
research. This resulted in the novel discovery that by controlling
the presence of the one or more components selected from the group
consisting of a fatty acid and a fatty acid amide such that the C
concentration obtained by X-ray photoelectron spectroscopy
conducted at a photoelectron take-off angle of 10 degrees on the
surface on the magnetic layer side of the magnetic tape (C
concentration (10 degrees)) was greater than or equal to 50 atom %,
it was possible to overcome the tradeoff and achieve both enhanced
resistance to scratching and reduced dropout. This point will be
described in greater detail below.
X-ray photoelectron spectroscopy is an analysis method that is
commonly referred to as electron spectroscopy for chemical analysis
(ESCA) or X-ray photoelectron spectroscopy (XPS). Hereinafter,
X-ray photoelectron spectroscopy will also be referred to as ESCA.
ESCA is an analysis method that exploits the fact that
photoelectrons are released when the surface of a sample being
measured is irradiated with X-rays. It is widely employed as an
analysis method for the surface layer portions of samples being
measured. ESCA makes it possible to employ the X-ray photoelectron
spectrum obtained by analysis of the surface of a sample being
measured to conduct qualitative and quantitative analysis. Within
the depth from the outer surface of the sample to the analysis
position (also referred to hereinafter as the "detection depth")
and the photoelectron take-off angle, the following equation
generally holds true: detection depth is nearly equal to .apprxeq.
(nearly equal to) average free path of electrons.times.3.times.sin
.theta.. In the equation, the detection depth is the depth at which
95% of the photoelectrons constituting the X-ray photoelectron
spectrum are generated and .theta. is the photoelectron take-off
angle. From the above equation, it will be understood that the
smaller the photoelectron take-off angle, the shallower the depth
from the sample surface that can be analyzed, and the larger the
photoelectron take-off angle, the deeper the depth from the surface
that can be analyzed. In analysis by ESCA at a photoelectron
take-off angle of 10 degrees, a surface layer portion of only
several nm in depth from the surface of the sample is normally the
position analyzed. Accordingly, analysis by ESCA conducted at a
photoelectron take-off angle of 10 degrees on the surface of the
magnetic tape permits compositional analysis of an extreme outer
layer portion of only about several nm in depth from the surface of
the magnetic tape.
Additionally, the C concentration that is obtained by X-ray
photoelectron spectroscopic analysis is the proportion accounted
for by carbon atoms C detected from the peak area of the C1s
spectrum of the total (based on atoms) 100 atom % of all elements
detected in qualitative analysis by ESCA. The above magnetic tape
contains one or more components selected from the group comprised
of a fatty acid and a fatty acid amide in at least the magnetic
layer. In a magnetic tape containing one or more of these
components in the magnetic layer, the C concentration (10 degrees)
obtained by ESCA analysis at a photoelectron take-off angle of 10
degrees is assumed by the present inventors to be an indicator of
the quantity of these components (one or more components selected
from the group consisting of a fatty acid and a fatty acid amide)
that is present in the extreme outer layer portion of the magnetic
layer.
Research conducted by the present inventors has revealed that a
magnetic tape with a C concentration (10 degrees) of greater than
or equal to 50 atom % can develop few scratches even with repeated
running and can exhibit good resistance to scratching. The present
inventors assume that this may be due to the fact that in a
magnetic tape comprising one or more components selected from the
group consisting of a fatty acid and a fatty acid amide in at least
the magnetic layer and having a C concentration (10 degrees) of
greater than or equal to 50 atom %, the components are present in
larger quantity in the extreme outer layer portion of the magnetic
layer than in conventional magnetic tapes despite the fact that the
quantities of the compounds selected from the group consisting of a
fatty acid and a fatty acid amide as set forth above have been
reduced. By contrast, investigation by the present inventors has
revealed that the formation of a lubricant layer on the surface of
the magnetic layer by coating (overcoating) a lubricant on the
surface of the magnetic layer as is described in the above
publication, Japanese Unexamined Patent Publication (KOKAI) No.
2008-243317, makes it difficult to obtain a magnetic tape with a C
concentration (10 degrees) of greater than or equal to 50 atom %
using the technique described in the publication because the
lubricant that is overcoated may permeate the interior of the
magnetic layer.
The above are what the present inventors presume to be the reasons
for which the above magnetic tape can exhibit reduced scratching in
repeated running and the reduced occurrence of dropout during
signal reading. However, these are merely presumptions, and do not
limit the present invention in any way.
The above magnetic tape will be described in greater detail
below.
<Magnetic Layer Side Surface Extraction Quantity>
In the present invention, the quantity of components selected from
the group consisting of a fatty acid and a fatty acid amide per
unit area of the magnetic tape in the extraction components
extracted from the surface on the magnetic layer side of the
magnetic tape (the magnetic layer side surface extraction quantity)
is a value that is measured by the following method.
The above extraction components refer to the components extracted
from a sample, obtained by cutting 5 cm at any position in the
longitudinal direction of a magnetic tape, by immersion with
heating in 30 mL of methanol for 3 hours at 60.degree. C. (solution
temperature). As described further below, when the magnetic tape
has a backcoat layer, the above extraction is conducted after
removing the backcoat layer prior to cutting out the sample.
Subsequently, the methanol is evaporated from the components that
have been extracted and gas chromatography is employed to conduct
qualitative and quantitative analysis. The contents of the various
fatty acids and fatty acid amides in the extraction components are
thus obtained. The values obtained are divided by the surface area
of the magnetic tape (the surface on the magnetic layer side) of
the sample to calculate the quantity of fatty acid and the quantity
of fatty acid amide per unit area of the magnetic tape. The values
calculated are then added together to obtain the magnetic layer
side surface extraction quantity.
The magnetic layer side surface extraction quantity that is
obtained by the above method is thought by the present inventors to
be a value that can serve as an indicator of the quantity of
components selected from the group consisting of a fatty acid and a
fatty acid amide that are present in the magnetic tape (bulk).
Investigation by the present inventors has resulted in the novel
discovery that little dropout occurs during signal reading on a
tape in which the magnetic layer side surface extraction quantity
is less than or equal to 15.0 mg/m.sup.2. From the perspective of
further decreasing dropout, the magnetic layer side surface
extraction quantity is desirably less than or equal to 12.0
mg/m.sup.2, preferably less than or equal to 11.5 mg/m.sup.2, and
more preferably, less than or equal to 11.0 mg/m.sup.2. The
magnetic layer side surface extraction quantity can be, for
example, greater than or equal to 5.0 mg/m.sup.2 or greater than or
equal to 7.0 mg/m.sup.2. However, since it suffices for the
components selected from the group consisting of a fatty acid and a
fatty acid amide to be present in a state in which the C
concentration (10 degrees) is greater than or equal to 50 atom %,
the lower limit is not set to those levels. The quantity of a fatty
acid and the quantity of a fatty acid amide that are extracted from
the surface of the magnetic layer side of the magnetic tape by the
method set forth above can be as follows. For example, the fatty
acid extraction quantity can be less than or equal to 14.0
mg/m.sup.2, less than or equal to 13.0 mg/m.sup.2, or less than or
equal to 12.0 mg/m.sup.2, and greater than or equal to 0
mg/m.sup.2, greater than or equal to 3.0 mg/m.sup.2, or greater
than or equal to 5.0 mg/m.sup.2. As a further example, the fatty
acid amide extraction quantity can be less than or equal to 5.0
mg/m.sup.2, less than or equal to 4.0 mg/m.sup.2, or less than or
equal to 3.0 mg/m.sup.2, and greater than or equal to 0 mg/m.sup.2,
greater than or equal to 0.1 mg/m.sup.2, or greater than or equal
to 0.3 mg/m.sup.2. However, both the fatty acid and the fatty acid
amide can be thought of as components exhibiting the same effect as
boundary lubricants as set forth further below. Thus, the
extraction quantities of the various components are not limited to
the above ranges; less than or equal to 15.0 mg/m.sup.2 will
suffice as the magnetic layer side surface extraction quantity. The
magnetic layer side surface extraction quantity can be controlled
by means of the quantity of components selected from the group
consisting of a fatty acid and a fatty acid amide that is added to
either, or both, the magnetic layer forming composition and the
nonmagnetic layer forming composition.
<C Concentration Obtained by ESCA Analysis>
The C concentration (10 degrees) of the magnetic tape is greater
than or equal to 50 atom %. When the C concentration (10 degrees)
is greater than or equal to 50 atom %, good resistance to
scratching can be achieved. Based on investigation by the present
inventors, when the C concentration (10 degrees) falls within a
range of greater than or equal to 50 atom %, good resistance to
scratching can be achieved even if the value rises. Accordingly,
for this reason, no upper limit is established for the C
concentration (10 degrees). By way of example, the upper limit can
be less than or equal to 95 atom %, less than or equal to 90 atom
%, less than or equal to 85 atom %, or less than or equal to 80
atom %. Additionally, based on investigation by the present
inventors, it is desirable from the perspective of obtaining a
magnetic tape with a highly smooth surface for the C concentration
(10 degrees) to be less than or equal to 80 atom %. For this
reason, the C concentration (10 degrees) is desirably less than or
equal to 80 atom %, preferably less than or equal to 70 atom %, and
more preferably, less than or equal to 65 atom %.
The above C concentration (10 degrees) is a value that is obtained
by compositional analysis of the extreme outer layer portion of the
magnetic layer side surface of the magnetic tape as set forth
above. In one embodiment of the magnetic tape, it is desirable for
one or more components selected from the group consisting of a
fatty acid and a fatty acid amide to be locally present in the
extreme outer layer portion of the magnetic layer side surface.
That is because, as set forth above, to increase resistance to
scratching while reducing the quantity of the component selected
from the group consisting of a fatty acid and a fatty acid amide to
reduce dropout as set forth above, it is thought to be desirable
for the component to be locally present in the magnetic layer side
surface. Such a localized state can be confirmed in ESCA analysis
by employing a photoelectron take-out angle of greater than 10
degrees and confirming that the C concentration obtained by
compositional analysis of a relatively deep portion is lower than
the C concentration (10 degrees). For example, the C concentration
(C concentration (90 degrees)) obtained by X-ray photoelectron
spectroscopy conducted at a photoelectron take-out angle of 90
degrees can be confirmed to be lower than the C concentration (10
degrees). In one embodiment, the C concentration (90 degrees) is
desirably less than 50 atom %, preferably less than or equal to 45
atom %, and more preferably, less than or equal to 40 atom %. The C
concentration (90 degrees) is, for example, greater than or equal
to 30 atom %, but can be lower than 30 atom % if the C
concentration (10 degrees) and the magnetic layer side surface
extraction quantity are within the above-stated ranges.
As set forth above, the C concentration (10 degrees) is a value
that is obtained by ESCA analysis conducted at a photoelectron
take-out angle of 10 degrees. The area analyzed is an area of 300
.mu.m.times.700 .mu.m at some position on the magnetic layer side
surface of the magnetic tape. ESCA qualitative analysis is
conducted by wide scan measurement (pass energy: 160 eV, scan
range: 0 to 1,200 eV, energy resolution: 1 eV/step). Next, the
spectra of all of the elements detected by qualitative analysis are
obtained by narrow scan measurement (pass energy: 80 eV, energy
resolution: 0.1 eV, scan range: set for each element so that the
entire spectrum being measured will fit). From the peak areas of
the various spectra thus obtained, the atomic concentrations (unit:
atom %) of the various elements are computed. Here, the atomic
concentration (C concentration) of carbon atoms is calculated from
the peak area of the C1s spectrum. The C concentration (90 degrees)
can be obtained in the same manner as above with the exception of
the photoelectron take-out angle being 90 degrees.
A desirable way to adjust the C concentration (10 degrees) set
forth above to greater than or equal to 50 atom % for example is to
implement a cooling step in the nonmagnetic layer forming step
described in detail further below. A desirable way to render the C
concentration (90 degrees) lower than the C concentration (10
degrees) is to implement this cooling step, for example. However,
the magnetic tape of an aspect of the present invention is not
limited to being manufactured with such a cooling step.
<Fatty Acid and Fatty Acid Amide>
The above magnetic tape contains one or more components selected
from the group consisting of a fatty acid and a fatty acid amide in
at least the magnetic layer. It is possible to incorporate either a
fatty acid or a fatty acid amide, or to incorporate both, into the
magnetic layer. As set forth above, these components are assumed by
the present inventors to contribute to enhancing resistance to
scratching by being present in large quantities in the extreme
outer layer portion of the magnetic layer. One or more components
selected from the group consisting of a fatty acid and a fatty acid
amide can be contained in the nonmagnetic layer. Either a fatty
acid or fatty acid amide, or both, can also be contained in the
nonmagnetic layer.
Examples of the fatty acid are lauric acid, myristic acid, palmitic
acid, stearic acid, oleic acid, linoleic acid, linolenic acid,
behenic acid, erucic acid, and elaidic acid. Stearic acid, myristic
acid, and palmitic acid are desirable, and stearic acid is
preferred. The fatty acid can also be incorporated into the
magnetic layer in the form of salts such as metal salts.
Examples of the fatty acid amide are amides of various fatty acids,
such as amide laurate, amide myristate, amide palmitate, and amide
stearate.
For the fatty acid and fatty acid derivatives (amides, esters
described further below, and the like), the fatty acid derived
moiety of a fatty acid derivative desirably has a structure that is
identical or similar to that of the fatty acid which is employed
together. As an example, when employing stearic acid as a fatty
acid, it is desirable to employ amide stearate and/or stearic acid
ester.
The quantity of fatty acid can be, for example 0.1 to 10.0 weight
parts, desirably 1.0 to 7.0 weight parts, per 100.0 weight parts of
ferromagnetic powder as the content in the magnetic layer forming
composition. When two or more different fatty acids are added to
the magnetic layer forming composition, the content refers to the
combined content thereof. Unless specifically stated otherwise,
this similarly applies to the contents of other components in the
this specification.
The content of fatty acid amide in the magnetic layer forming
composition can be, for example, 0.1 to 3.0 weight parts, desirably
0.1 to 1.0 weight parts, per 100.0 weight parts of ferromagnetic
powder.
Additionally, the fatty acid content in the nonmagnetic layer
forming composition is, for example, 1.0 to 10.0 weight parts,
desirably 1.0 to 7.0 weight parts, per 100.0 weight parts of
nonmagnetic powder. The content of fatty acid amide in the
nonmagnetic layer forming composition is, for example, 0.1 to 3.0
weight parts, desirably 0.1 to 1.0 weight parts, per 100.0 weight
parts of nonmagnetic powder.
<Fatty Acid Ester>
A fatty acid ester can be incorporated, or not incorporated, into
one or both the magnetic layer and nonmagnetic layer, which is
described in detail further below.
The present inventors presume that the component selected from the
group consisting of a fatty acid and a fatty acid amide can
contribute to enhancing resistance to scratching. The fatty acid
ester is also components that can function as lubricants, but the
present inventors presume that the fatty acid ester does not have
an effect (or have only a slight effect) on scratch resistance in a
magnetic tape with a magnetic layer side surface extraction
quantity of less than or equal to 15.0 mg/m.sup.2. Lubricants can
generally be broadly divided into fluid lubricants and boundary
lubricants. The fatty acid ester is a component that can function
as fluid lubricants, while the fatty acid amide and the fatty acid
are components that cab function as boundary lubricants. Boundary
lubricants can be thought of as lubricants that are capable of
decreasing contact friction by adsorbing to the surface of powder
(such as ferromagnetic powder) and forming a strong lubricating
film. Conversely, fluid lubricants can be thought of as lubricants
that form liquid films themselves on the surface of magnetic layers
and reduce friction through the flow of the liquid film. Thus, the
fact that the fatty acid and the fatty acid amide have a different
action as lubricants is thought by the present inventors to be why
the fatty acid ester has a different effect in scratch resistance
than the fatty acid and the fatty acid amide. The fatty acid ester
is a lubricant that generally can contribute to enhancing the
running durability of magnetic tapes. Thus, for example, the fatty
acid ester can be incorporated into either the magnetic layer or
the nonmagnetic layer, described further below, or both, to enhance
running durability.
Examples of the fatty acid ester are esters of the various fatty
acids set forth above, such as butyl myristate, butyl palmitate,
butyl stearate, neopentyl glycol dioleate, sorbitan monostearate,
sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl
stearate, isotridecyl stearate, octyl stearate, isooctyl stearate,
amyl stearate, and butoxyethyl stearate.
The quantity of fatty acid ester is, for example, 0 to 10.0 weight
parts, desirably 1.0 to 7.0 weight parts, per 100.0 weight parts of
ferromagnetic powder as the content in the magnetic layer forming
composition.
The content of fatty acid ester in the nonmagnetic layer forming
composition is, for example, 0 to 10.0 weight parts, desirably 1.0
to 7.0 weight parts, per 100.0 weight parts of nonmagnetic
powder.
The magnetic layer, nonmagnetic layer, and the like of the above
magnetic tape will be described next in greater detail.
<Magnetic Layer>
(Ferromagnetic Powder)
Various powders that are commonly employed as ferromagnetic powder
in the magnetic layers of magnetic tapes can be employed as the
ferromagnetic powder. The use of ferromagnetic powder of small
average particle size is desirable from the perspective of
enhancing the recording density of the magnetic tape. To that end,
the ferromagnetic powder with an average particle size of less than
or equal to 50 nm is desirably employed. From the perspective of
the stability of magnetization, the ferromagnetic powder with an
average particle size of greater than or equal to 10 nm is
desirably employed.
The average particle size of the ferromagnetic powder is a value
measured with a transmission electron microscope by the following
method.
Ferromagnetic powder is photographed at a magnification of
100,000-fold with a transmission electron microscope, and the
photograph is printed on print paper at a total magnification of
500,000-fold to obtain a photograph of the particles constituting
the ferromagnetic powder. A target particle is selected from the
photograph of particles that has been obtained, the contour of the
particle is traced with a digitizer, and the size of the (primary)
particle is measured. The term "primary particle" refers to an
unaggregated, independent particle.
The above measurement is conducted on 500 randomly extracted
particles. The arithmetic average of the particle size of the 500
particles obtained in this manner is adopted as the average
particle size of the ferromagnetic powder. A Model H-9000
transmission electron microscope made by Hitachi can be employed as
the above transmission electron microscope, for example. The
particle size can be measured with known image analysis software,
such as KS-400 image analysis software from Carl Zeiss.
In the present invention, the average particle size of the powder,
such as ferromagnetic powder and various kinds of powder, is the
average particle size as obtained by the above method. The average
particle size indicated in Examples further below was obtained
using a Model H-9000 transmission electron microscope made by
Hitachi and KS-400 image analysis software made by Carl Zeiss.
The method described in paragraph 0015 of Japanese Unexamined
Patent Publication (KOKAI) No. 2011-048878, which is expressly
incorporated herein by reference in its entirety, for example, can
be employed as the method of collecting sample powder such as
ferromagnetic powder from a magnetic layer for particle size
measurement.
In the present invention, the size of the particles constituting
powder such as ferromagnetic powder (referred to as the "particle
size", hereinafter) is denoted as follows based on the shape of the
particles observed in the above particle photograph: (1) When
acicular, spindle-shaped, or columnar (with the height being
greater than the maximum diameter of the bottom surface) in shape,
the particle size is denoted as the length of the major axis
constituting the particle, that is, the major axis length. (2) When
platelike or columnar (with the thickness or height being smaller
than the maximum diameter of the plate surface or bottom surface)
in shape, the particle size is denoted as the maximum diameter of
the plate surface or bottom surface. (3) When spherical,
polyhedral, of unspecific shape, or the like, and the major axis
constituting the particle cannot be specified from the shape, the
particle size is denoted as the diameter of an equivalent circle.
The term "diameter of an equivalent circle" means that obtained by
the circle projection method.
The "average acicular ratio" of a powder refers to the arithmetic
average of values obtained for the above 500 particles by measuring
the length of the minor axis, that is the minor axis length, of the
particles measured above, and calculating the value of the (major
axis length/minor axis length) of each particle. The term "minor
axis length" refers to, in the case of the particle size definition
of (1), the length of the minor axis constituting the particle; in
the case of (2), the thickness or height, and in the case of (3),
since the major axis and minor axis cannot be distinguished, (major
axis length/minor axis length) is deemed to be 1 for the sake of
convenience.
When the particle has a specific shape, such as in the particle
size definition of (1) above, the average particle size is the
average major axis length. In the case of (2), the average particle
size is the average plate diameter, with the average plate ratio
being the arithmetic average of (maximum diameter/thickness or
height). For the definition of (3), the average particle size is
the average diameter (also called the average particle
diameter).
Ferromagnetic hexagonal ferrite powder is a specific example of
desirable ferromagnetic powder. From the perspectives of achieving
higher density recording and magnetization stability, the average
particle size (average plate diameter) of ferromagnetic hexagonal
ferrite powder desirably ranges from 10 nm to 50 nm, preferably 20
nm to 50 nm. Reference can be made to Japanese Unexamined Patent
Publication (KOKAI) No. 2011-225417, paragraphs 0012 to 0030,
Japanese Unexamined Patent Publication (KOKAI) No. 2011-216149,
paragraphs 0134 to 0136, and Japanese Unexamined Patent Publication
(KOKAI) No. 2012-204726, paragraphs 0013 to 0030, for details on
ferromagnetic hexagonal ferrite powder. The contents of the above
publications are expressly incorporated herein by reference in
their entirety.
Ferromagnetic metal powder is also a specific example of desirable
ferromagnetic powder. From the perspectives of achieving higher
density recording and magnetization stability, the average particle
size (average major axis length) of ferromagnetic metal powder
desirably ranges from 10 nm to 50 nm, preferably 20 nm to 50 nm.
Reference can be made to Japanese Unexamined Patent Publication
(KOKAI) No. 2011-216149, paragraphs 0137 to 0141, and Japanese
Unexamined Patent Publication (KOKAI) No. 2005-251351, paragraphs
0009 to 0023, for details on ferromagnetic metal powder. The
contents of the above publications are expressly incorporated
herein by reference in their entirety.
(Binder, Curing Agent)
The magnetic tape according to an aspect of the present invention
is a particulate magnetic tape that contains binder along with
ferromagnetic powder in the magnetic layer. Polyurethane resins,
polyester resins, polyamide resins, vinyl chloride resins, acrylic
resins such as those provided by copolymerizing styrene,
acrylonitrile, methyl methacrylate and the like, cellulose resins
such as nitrocellulose, epoxy resins, phenoxy resins,
polyvinylacetal, polyvinylbutyral, and other polyvinyl alkylal
resins can be employed singly, or as mixtures of multiple resins,
as the binder contained in the magnetic layer. Among these,
desirable resins are polyurethane resin, acrylic resins, cellulose
resins, and vinyl chloride resins. These resins can also be
employed as binders in the nonmagnetic layer described further
below. Reference can be made to paragraphs 0028 to 0031 of Japanese
Unexamined Patent Publication (KOKAI) No. 2010-24113, which is
expressly incorporated herein by reference in its entirety, with
regard to the above binders.
Further, a curing agent can be employed along with the resin
suitable for use as the binder. Polyisocyanate is suitable as the
curing agent. Reference can be made to paragraphs 0124 to 0125 in
Japanese Unexamined Patent Publication (KOKAI) No. 2011-216149, for
details regarding polyisocyanates. The curing agent can be added to
the magnetic layer forming composition in a quantity of, for
example, 0 to 80.0 weight parts, preferably 50.0 weight parts to
80.0 weight parts from the perspective of enhancing the coating
strength, per 100.0 weight parts of binder.
(Additive)
Additives can be added to the magnetic layer as needed. Examples of
additives are abrasives, dispersing agents and dispersion
adjuvants, antifungal agents, antistatic agents, oxidation
inhibitors, and carbon black. The additives can be selected for use
from among commercial products based on the desired properties.
It is desirable to increase the smoothness of the magnetic layer
side surface in magnetic tapes for high-density recording, such as
data backup tapes. By increasing the smoothness of the magnetic
layer side surface, it is possible to reduce spacing loss. As a
result, it is possible to achieve good electromagnetic
characteristics during the reproduction of a signal recorded at
high density. From these perspectives, the magnetic tape of an
aspect of the present invention also desirably has a magnetic layer
with a highly smooth surface.
In one embodiment, the centerline average surface roughness Ra as
measured with a noncontact surface profiler on the magnetic layer
side surface of the magnetic tape can be employed as an indicator
of the surface smoothness of the magnetic layer side surface of the
magnetic tape. The centerline average surface roughness Ra as
measured by a noncontact surface profiler refers to the centerline
average surface roughness Ra measured in a region with an area of
350 .mu.m.times.260 .mu.m of the magnetic layer side surface of the
magnetic tape using a 20.times. objective lens. An optical
three-dimensional roughness meter, for example, can be employed as
the noncontact surface profiler. As an example of a measurement
device, a noncontact optical roughness measuring device in the form
of a Newview (Japanese registered trademark) 5022 made by Zygo can
be employed.
From the perspective of reducing spacing loss, the centerline
average surface roughness Ra that is measured by the noncontact
surface profiler on the magnetic layer surface of the magnetic tape
is desirably less than or equal to 1.8 nm, preferably less than or
equal to 1.7 nm, more preferably less than or equal to 1.6 nm, and
still more preferably, less than or equal to 1.5 nm. From the
perspective of running stability, the Ra is desirably greater than
or equal to 0.2 nm.
As set forth above, it is desirable from the perspective of
increasing the surface smoothness of the magnetic layer side
surface of the magnetic tape for the C concentration (10 degrees)
to be less than or equal to 80 atom %, preferably less than or
equal to 70 atom %, and more preferably, less than or equal to 65
atom %.
An example of one way to increase the surface smoothness of the
magnetic layer side surface of the magnetic tape is to increase the
dispersion of abrasive in the magnetic layer. To that end, it is
desirable to separately disperse the abrasive from the
ferromagnetic powder in preparing the magnetic layer forming
composition. It is preferable to separately disperse the abrasive
from various granular or powder components such as the
ferromagnetic powder in preparing the magnetic layer forming
composition.
Another example of a way of increasing the smoothness of the
surface of the magnetic layer is to employ a component
(abrasive-dispersing agent) to increase the dispersion of the
abrasive. An example of such a component is an aromatic hydrocarbon
compound having a phenolic hydroxyl group. The term "phenolic
hydroxyl group" refers to a hydroxyl group that is directly bonded
to an aromatic ring.
The aromatic ring that is contained in the aromatic hydrocarbon
compound having a phenolic hydroxyl group can be a single ring, can
have a multiple-ring structure, or can be a fused ring. From the
perspective of enhancing the dispersion of abrasive, an aromatic
hydrocarbon compound comprising a benzene ring or a naphthalene
ring is desirable. The aromatic hydrocarbon compound can comprise
substituent(s) in addition to the phenolic hydroxyl group. From the
perspective of the ready availability of compounds, examples of
substituents in addition to a phenolic hydroxyl group are halogen
atoms, alkyl groups, alkoxy groups, amino groups, acyl groups,
nitro groups, nitroso groups, and hydroxyalkyl groups. With respect
to compounds having substituent(s) in addition to the phenolic
hydroxyl group, compounds having substituent(s) exhibiting an
electron donating ability in the form of a Hammett substituent
constant of less than or equal to 0.4 tend to be advantageous to
the dispersion of abrasives. From this perspective, examples of
desirable substituents are those having an electron-donating
ability that is as good as or better than that of halogen atoms,
more specifically, halogen atoms, alkyl groups, alkoxy groups,
amino groups, and hydroxyalkyl groups.
The number of phenolic hydroxyl groups that are contained in the
above aromatic hydrocarbon compound can be one, two, three, or
more. When the aromatic ring present in the aromatic hydrocarbon
compound is a naphthalene ring, it is desirable for two or more
phenolic hydroxyl groups to be contained, preferably two. Examples
of such compounds are the naphthalene ring-containing compounds
denoted by general formula (1) in Japanese Unexamined Patent
Publication (KOKAI) No. 2013-229090. Reference can be made to
paragraphs 0028 to 0030 of that publication for details on
naphthalene ring-containing compounds denoted by general formula
(1) in Japanese Unexamined Patent Publication (KOKAI) No.
2013-229090. Additionally, aromatic hydrocarbon compounds
containing an aromatic ring in the form of a benzene ring desirably
contain one or more, preferably 1 or 2, phenolic hydroxyl groups.
Examples of such compounds are the benzene ring-containing
compounds denoted by general formula (2) in Japanese Unexamined
Patent Publication (KOKAI) No. 2013-229090. Reference can be made
to paragraphs 0032 to 0034 of that publication for details on
benzene ring-containing compounds denoted by general formula (2) in
Japanese Unexamined Patent Publication (KOKAI) No. 2013-229090. The
content of the above publication is expressly incorporated herein
by reference in its entirety.
One, two, or more aromatic hydrocarbon compounds having phenolic
hydroxyl group(s) can be employed. The quantity employed is, for
example, desirably about 2.0 to 20.0 weight parts per 100.0 weight
parts of abrasive.
It is desirable to employ inorganic powder with Mohs hardness of
higher than 8, and preferable to employ inorganic powder with Mohs
hardness greater than or equal to 9, as an abrasive. The highest
Mohs hardness is the 10 of diamond. Specific examples are alumina
(Al.sub.2O.sub.3), silicon carbide, boron carbide (B.sub.4C), TiC,
cerium oxide, zirconium oxide (ZrO.sub.2), and diamond powder. Of
these, alumina is desirable. Alumina is also a desirable abrasive
from the perspective of being able to achieve particularly good
dispersion improvement when combined with the above aromatic
hydrocarbon compound having phenolic hydroxyl group(s). Reference
can be made to Japanese Unexamined Patent Publication (KOKAI) No.
2013-229090, paragraph 0021, with regard to alumina. The specific
surface area can be employed as an indicator of abrasive particle
size. The larger the specific surface area, the smaller the
particle size indicated. From the perspective of increasing the
smoothness of the surface of the magnetic layer, an abrasive having
a specific surface area measured by the BET method (BET specific
surface area) of greater than or equal to 14 m.sup.2/g is desirably
employed. From the perspective of dispersion, the use of an
abrasive with a BET specific surface area of less than or equal to
40 m.sup.2/g is desirably employed. The content of abrasive in the
magnetic layer is desirably 1.0 to 20.0 weight parts per 100.0
weight parts of ferromagnetic powder.
The magnetic layer can contain granular nonmagnetic materials
(nonmagnetic particles). From the perspective of increasing the
surface smoothness of the magnetic layer side surface, colloidal
particles (nonmagnetic colloidal particles) are desirable as the
nonmagnetic particles. The average primary particle size of
nonmagnetic colloidal particles is desirably 50 to 200 nm. The
average primary particle size of the nonmagnetic colloidal
particles in the present invention is a value obtained by the
method described in Japanese Unexamined Patent Publication (KOKAI)
No. 2011-48878, paragraph 0015. The content of the above
publication is expressly incorporated herein by reference in its
entirety. Nonmagnetic colloidal particles in the form of inorganic
colloidal particles are desirable and those in the form of
inorganic oxide colloidal particles are preferred. From the
perspective of ready availability of monodisperse colloidal
particles, silica colloidal particles (colloidal silica) are
particularly desirable. Reference can be made to Japanese
Unexamined Patent Publication (KOKAI) No. 2011-48878, paragraph
0023, for details on nonmagnetic colloidal particles. The content
of nonmagnetic colloidal particles in the magnetic layer is
desirably 0.5 to 5.0 weight parts, preferably 1.0 to 3.0 weight
parts, per 100.0 weight parts of ferromagnetic powder.
The magnetic layer set forth above is provided on a magnetic
support over a nonmagnetic layer. Details regarding the nonmagnetic
layer and nonmagnetic support will be given further below.
<Nonmagnetic Layer>
The nonmagnetic layer will be described next. In the magnetic tape
according to an aspect of the present invention, a nonmagnetic
layer containing nonmagnetic powder and binder is present between
the nonmagnetic support and the magnetic layer. The nonmagnetic
powder that is employed in the nonmagnetic layer can be an organic
or an inorganic substance. Carbon black or the like can also be
employed. Examples of inorganic materials are metals, metal oxides,
metal carbonates, metal sulfates, metal nitrides, metal carbides,
and metal sulfides. These nonmagnetic powders are available as
commercial products and can be manufactured by known methods.
Reference can be made to Japanese Unexamined Patent Publication
(KOKAI) No. 2011-216149, paragraphs 0146 to 0150, for details.
Reference can be made to Japanese Unexamined Patent Publication
(KOKAI) No. 2010-24113, paragraphs 0040 and 0041, for details on
carbon black that can be used in the nonmagnetic layer.
The fatty acid, fatty acid amide, and fatty acid ester that can be
contained in the nonmagnetic layer are as set forth above. The
binder, additives, dispersion method, and the like of the magnetic
layer can also be applied to the nonmagnetic layer. In particular,
techniques that are known with regard to the magnetic layer can be
applied with regard to the quantity and type of binder and quantity
and type of additives.
The nonmagnetic layer can be formed by coating and drying the
nonmagnetic layer forming composition on the nonmagnetic layer, the
details of which will be described further below. Normally, one or
more solvents are contained. Various organic solvents that are
generally employed in the manufacturing of particulate magnetic
recording media are examples of the solvent. Specifically, the
following can be employed in any ratio: ketones such as acetone,
methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone,
cyclohexanone, isophorone, and tetrahydrofuran; alcohols such as
methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl
alcohol, and methyl cyclohexanol; esters such as methyl acetate,
butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate,
and glycol acetate; glycol ethers such as glycol dimethyl ether,
glycol monoethyl ether, and dioxane; aromatic hydrocarbons such as
benzene, toluene, xylene, cresol, and chlorobenzene; chlorinated
hydrocarbons such as methylene chloride, ethylene chloride, carbon
tetrachloride, chloroform, ethylene chlorohydrin, and
dichlorobenzene; N,N-dimethyl formamide; and hexane. Of these, from
the perspective of solubility of the binders that are commonly
employed in particulate magnetic recording media, one or more
ketone solvent is desirably incorporated. The quantity of solvent
in the nonmagnetic layer forming composition is not specifically
limited. The same quantity can be employed as in the nonmagnetic
layer forming composition of a common particulate magnetic
recording medium.
Further, the description given above can be applied for solvents
that can be incorporated in the various layer forming compositions
such as the magnetic layer forming composition.
<Nonmagnetic Support>
The nonmagnetic support will be described next. Known nonmagnetic
supports in the form of biaxially stretched polyethylene
terephthalate, polyethylene naphthalate, polyamide,
polyamide-imide, aromatic polyamide, and the like are examples. Of
these, polyethylene terephthalate, polyethylene naphthalate, and
polyamide are desirable. These supports can be subjected in advance
to treatments such as corona discharge, plasma treatments,
adhesion-enhancing treatments, and heat treatments.
<Layer Structure>
As regards the thickness of the nonmagnetic support and the various
layers in the magnetic tape of an aspect of the present invention,
the thickness of the nonmagnetic support is desirably 3.00 .mu.m to
4.50 .mu.m. The thickness of the magnetic layer can be optimized
based on the magnetization saturation level of the magnetic head
employed, the head gap length, and the recording signal band.
Generally, it will be 10 nm to 150 nm. From the perspective of
achieving higher density recording, it is desirably 20 nm to 120
nm, preferably 30 nm to 100 nm. A single magnetic layer suffices.
The magnetic layer can be separated into two or more layers having
differing magnetic properties. Known multilayer magnetic layer
configurations can be applied.
The thickness of the nonmagnetic layer is, for example, 0.01 .mu.m
to 3.00 .mu.m, desirably 0.05 .mu.m to 2.00 .mu.m, and preferably,
0.05 .mu.m to 1.50 .mu.m.
As regards the magnetic tape, to increase the recording capacity
per magnetic tape cartridge, the overall thickness of the magnetic
tape is desirably reduced (that is, the magnetic tape can be
thinned) to increase the total length of the tape that is housed in
each magnetic tape cartridge. To achieve this thinning, it has
conventionally been effective to reduce the thickness of the
nonmagnetic layer that accounted for a large proportion of the
thickness of the various layers provided in a magnetic tape. From
this perspective, in one embodiment of the above magnetic tape, the
thickness of the nonmagnetic layer is desirable kept to within a
range of 0.05 .mu.m to 0.60 .mu.m, preferably to within a range of
0.05 .mu.m to 0.40 .mu.m. As regards the occurrence of dropout set
forth above, the present inventors assume that the nonmagnetic
layer may soften when large quantities of a fatty acid or a fatty
acid amide are incorporated into a thin nonmagnetic layer, becoming
a factor in the occurrence of dropout. For this reason, the content
of the component selected from the group consisting of a fatty acid
and a fatty acid amide in the magnetic tape can be reduced so that
the magnetic layer side surface extraction quantity becomes less
than or equal to 15 mg/m.sup.2, as stated above. This fact is
presumed by the present inventors to be an effective means of
inhibiting the occurrence of dropout in a magnetic tape having a
thin nonmagnetic layer.
The nonmagnetic layer of the magnetic tape according to an aspect
of the present invention may be in the form of an essentially
nonmagnetic layer containing small quantities of ferromagnetic
powder, either in the form of impurities or by intention, for
example, along with nonmagnetic powder. In the present invention,
the term "essentially nonmagnetic layer" refers to a layer with a
residual magnetic flux density of less than or equal to 10 mT, a
coercive force of less than or equal to 7.96 kA/m (100 Oe), or a
layer with a residual magnetic flux density of less than or equal
to 10 mT and a coercive force of less than or equal to 7.96 kA/m
(100 Oe). The nonmagnetic layer desirably has neither residual
magnetic flux density nor coercive force.
<Backcoat Layer>
In the magnetic tape according to an aspect of the present
invention, a backcoat layer can be present on the opposite surface
of the nonmagnetic support from the surface on which the magnetic
layer is present. The backcoat layer desirably contains carbon
black and inorganic powder. The formulas of the magnetic layer and
nonmagnetic layer can be applied to the binder and various
additives for forming the backcoat layer. The thickness of the
backcoat layer is desirably less than or equal to 0.90 .mu.m,
preferably 0.10 to 0.70 .mu.m.
The thicknesses of the various layers and the nonmagnetic support
can be determined by known methods of measuring film thickness. For
example, a cross section of the magnetic tape in the direction of
thickness can be exposed by a known technique such as the use of an
ion beam or microtome, and the exposed cross-section can be
observed by a scanning electron microscope. The thickness can be
determined at one spot in the direction of thickness by
cross-section observation, or thicknesses determined at two or more
randomly selected spots--two spots, for example--can be
arithmetically averaged, to obtain the various thicknesses. The
thicknesses of various layers can also be obtained as design
thicknesses calculated from manufacturing conditions.
<Manufacturing Process>
(Preparation of Composition for Forming Each Layer)
Compositions (coating liquids) for forming the magnetic layer,
nonmagnetic layer, and backcoat layer normally contain solvent in
addition to the various components set forth above. The various
organic solvents that are commonly employed to manufacture
particulate magnetic tapes can be employed. The process of
preparing the compositions for forming the various layers normally
includes at least a kneading step, a dispersion step, and mixing
steps provided before and after these steps as needed. Each of
these steps can be divided into two or more stages. All of the
starting materials in the form of ferromagnetic powder, nonmagnetic
powder, fatty acid, fatty acid amide, binder, various optionally
added additives, solvent, and the like that are employed in the
present invention can be added at the start, or part way through,
any of these steps. An individual starting material can be divided
for addition in two or more steps. In preparing the composition for
forming the magnetic layer, as set forth above, it is desirable to
separately disperse the abrasive and ferromagnetic powder. An open
kneader, continuous kneader, pressurized kneader, extruder, or some
other device with powerful kneading force is desirably employed in
the kneading step. Details regarding these kneading processes are
given in Japanese Unexamined Patent Publication (KOKAI) Heisei Nos.
1-106338 and 1-79274, which are expressly incorporated herein by
reference in their entirety. Glass beads or some other form of bead
can be employed to disperse the compositions for forming the
various layers. High-density dispersion beads in the form of
zirconia beads, titania beads, and steel beads are suitable as such
dispersion beads. The particle diameter and fill rate of these
dispersion beads can be optimized for use. A known disperser can be
employed.
(Coating Step, Cooling Step, and Heating and Drying Step)
The magnetic layer can be formed by multilayer coating the magnetic
layer forming composition either successively or simultaneously
with the nonmagnetic layer forming composition. Reference can be
made to Japanese Unexamined Patent Publication (KOKAI) No.
2010-231843, paragraph 0066, for details regarding coating to form
the various layers. The content of the above publication is
expressly incorporated herein by reference in its entirety.
In one desirable embodiment, the magnetic tape of an aspect of the
present invention can be manufactured by sequential multilayer
coating. The manufacturing steps in sequential multilayer coating
are desirably conducted as follows. The nonmagnetic layer is formed
by a coating step of forming a coating layer of the nonmagnetic
layer forming composition on the nonmagnetic support by coating;
and a heating and drying step of drying by a heat treatment the
coating layer that has been formed. The magnetic layer forming
composition is then coated on the nonmagnetic layer that has been
formed in a coating step to form a coating layer, followed by a
heating and drying step of drying by a heat treatment the coating
layer that has been formed to form the magnetic layer.
In the manufacturing method by sequential multilayer coating, the
nonmagnetic layer forming step can be conducted using a nonmagnetic
layer forming composition containing one or more components
selected from the group consisting of a fatty acid and a fatty acid
amide in the coating step. Between the coating step and the heating
and drying step, it is desirable to conduct a cooling step of
cooling the coating layer to adjust the C concentration (10
degrees) to greater than or equal to 50 atom % in a magnetic tape
containing one or more components selected from the group
consisting of a fatty acid and a fatty acid amide in at least the
magnetic layer. Although the reasons for this are unclear, the
present inventors assume that cooling the coating layer of the
nonmagnetic layer forming composition prior to the heating and
drying step might facilitate migration of the above component
(fatty acid, fatty acid amide) onto the nonmagnetic layer surface
during solvent volatization in the heating and drying step.
However, this is merely conjecture, and does not limit the present
invention in any way.
That is, an aspect of the present invention relates to a method of
manufacturing the above magnetic tape, which comprises a step of
forming a nonmagnetic layer and a step of forming a magnetic layer,
wherein the step of forming the nonmagnetic layer comprises:
a coating step of forming a coating layer by coating on a
nonmagnetic support a nonmagnetic layer forming composition
comprising one or more components selected from the group
consisting of a fatty acid and afatty acid amide, nonmagnetic
powder, binder, and solvent;
a heating and drying step of drying the coating layer by a heat
treatment; and
the step of forming the nonmagnetic layer further comprises,
between the coating step and the heating and drying step, a cooling
step of cooling the coating layer.
In the step of forming the magnetic layer, a coating step of
forming a coating layer by coating on a nonmagnetic layer a
magnetic layer forming composition containing ferromagnetic powder,
binder, and solvent can be conducted, and a heating and drying step
of drying by a heat treatment the coating layer that has been
formed can be conducted. The magnetic tape of an aspect of the
present invention contains in at least the magnetic layer one or
more components selected from the group consisting of a fatty acid
and a fatty acid amide. It is desirable for the magnetic layer
forming composition to contain one or more components selected from
the group consisting of a fatty acid and a fatty acid amide to
manufacture the magnetic tape. However, it is not essential that
one or more components selected from the group consisting of a
fatty acid and a fatty acid amide be contained in the magnetic
layer forming composition. That is because it is conceivable to
form a magnetic layer containing one or more components selected
from the group consisting of a fatty acid and a fatty acid amide by
forming a magnetic layer by coating a magnetic layer forming
composition on a nonmagnetic layer after the component contained in
the nonmagnetic layer forming composition has migrated to the
surface of the nonmagnetic layer.
A specific embodiment of the manufacturing method will be described
below based on FIG. 1. However, the present invention is not
limited to the specific embodiment given below.
FIG. 1 is a schematic process diagram showing a specific embodiment
of the steps of manufacturing a magnetic tape having a backcoat
layer on the other surface of a nonmagnetic support from that on
which are sequentially present a nonmagnetic layer and a magnetic
layer. In the embodiment shown in FIG. 1, a nonmagnetic support
(long film) is continuously subjected to an operation of being fed
by a feeding part and being wound up in a winding part. In various
parts or various zones shown in FIG. 1, various processes such as
coating, drying, and orienting can be conducted to form by
sequential multilayer coating a nonmagnetic layer and a magnetic
layer on one surface of a nonmagnetic support that is running, and
a backcoat layer can be formed on the other surface. With the
exception of comprising a cooling zone, the manufacturing process
can be identical to the one that is commonly conducted to
manufacture a particulate magnetic recording medium.
In a first coating part, the nonmagnetic layer forming composition
is coated on the nonmagnetic support that has been fed from the
feeding part (step of coating the nonmagnetic layer coating
composition).
After the above coating step, the coating layer of the nonmagnetic
layer forming composition that has been formed in the coating step
is cooled in a cooling zone (cooling step). For example, the
cooling step can be conducted by having the nonmagnetic support on
which the coating layer has been formed pass through a cooling
atmosphere. The temperature of the cooling atmosphere desirably
falls within a range of -10.degree. C. to 0.degree. C., preferably
within a range of -5.degree. C. to 0.degree. C. The duration of the
cooling step (for example, the time from when some portion of the
coating layer is conveyed into the cooling zone to when it is
conveyed out, also referred to as the "residence time" hereinafter)
is not specifically limited. However, the longer it is, the higher
the C concentration (10 degrees) tends to be. Thus, it is desirable
adjusted, for example, based on preliminary testing based on the
necessity of achieving a C concentration (10 degrees) of greater
than or equal to 50 atom %. In the cooling step, a cooled gas can
be blown onto the surface of the coating layer.
After the cooling zone, in the first heat treatment zone, the
coating layer following the cooling step is dried by being heated
(heating and drying step). The heating and drying step can be
conducted by causing the nonmagnetic support on which the coating
layer is present following the cooling step to pass through a
heating atmosphere. Here, the temperature of the heating atmosphere
is, for example, about 60.degree. C. to 140.degree. C. However, any
temperature that will dry the coating layer by evaporating the
solvent will do, and there is no limit to the above range. A heated
gas can be optionally blown onto the surface of the coating layer.
The same holds true for the heating and drying step in the second
heat treatment zone and the heating and drying step in the third
heat treatment zone, described further below.
In the second coating part, the magnetic layer forming composition
is coated on the nonmagnetic layer that has been formed by the
heating and drying step in the first heat treatment zone (magnetic
layer forming composition coating step).
Subsequently, while the coating layer of the magnetic layer forming
composition is still wet, a step of orienting the ferromagnetic
powder in the coating layer is conducted in an orienting zone.
Reference can be made to Japanese Unexamined Patent Publication
(KOKAI) No. 2010-231843, paragraph 0067, with regard to orientation
processing.
The coating layer following the orientation processing is subjected
to a heating and drying step in a second heat treatment zone.
Then, in a third coating part, a backcoat layer forming composition
is coated to the surface on the opposite side of the nonmagnetic
support from the surface on which the nonmagnetic layer and
magnetic layer have been formed to form a coating layer (the
backcoat layer forming composition coating step). Subsequently, the
coating layer is heat treated and dried in a third heat treatment
zone.
A magnetic tape can be obtained with a nonmagnetic layer and
magnetic layer present in that order on one surface of a
nonmagnetic support, and a backcoat layer present on the other
surface. The magnetic tape obtained can be wound up on the winding
part and then optionally subjected to various post-processing
(various surface processing such as calendering). Known
post-processing techniques in the manufacturing of particulate
magnetic recording media can be applied without restriction. For
example, reference can be made to Japanese Unexamined Patent
Publication (KOKAI) No. 2010-231843, paragraph 0069, for a cutting
step that is normally conducted after various post-processing.
The magnetic tape of an aspect of the present invention that has
been set forth above is suitable for use as a magnetic tape
employed in both low-humidity environments and high-humidity
environments.
EXAMPLES
The present invention will be described in greater detail below
through Examples. However, the present invention is not limited to
the embodiments shown in Examples. The "parts" and "percent (%)"
indicated below denote "weight parts" and "weight percent (%)".
The weight average molecular weights given below are values
obtained by measurement by gel permeation chromatography (GPC)
under the following conditions with polystyrene conversion.
GPS device: HLC-8120 (made by Tosoh):
Column: TSK gel Multipore HXL-M (made by Tosoh, 7.8 mm ID (inner
diameter).times.30.0 cm)
Eluent: Tetrahydrofuran (THF)
Examples 1 to 14, Comparative Examples 1 to 19
1. Preparation of Alumina Dispersion
To 100.0 parts of alumina powder (HIT-80 made by Sumitomo Chemical
Co.) with an alpha conversion rate of about 65% and a BET specific
surface area of 20 m.sup.2/g were admixed 3.0 parts of
2,3-dihydroxynaphthalene (made by Tokyo Kasei), 31.3 parts of a 32%
solution (in a solvent in the form of a mixed solvent of methyl
ethyl ketone and toluene) of polyester polyurethane resin (UR-4800
made by Toyobo (Japanese registered trademark) with polar groups in
the form of SO.sub.3Na groups (polar group quantity: 80 meq/kg)),
and 570.0 parts of a solvent in the form of a mixed solution of 1:1
(weight ratio) methyl ethyl ketone and cyclohexanone. The mixture
was dispersed for 5 hours in a paint shaker in the presence of
zirconia beads. Following dispersion, the dispersion and the beads
were separated with a mesh, yielding an alumina dispersion.
2. Formula of Magnetic Layer Forming Composition
TABLE-US-00001 (Magnetic liquid) Ferromagnetic powder 100.0 parts
Ferromagnetic hexagonal barium ferrite powder or ferromagnetic
metal powder (see Table 5) Polyurethane resin containing SO.sub.3Na
groups 14.0 parts Weight average molecular weight: 70,000;
SO.sub.3Na groups: 0.2 meq/g Cyclohexanone 150.0 parts Methyl ethyl
ketone 150.0 parts (Abrasive liquid) Alumina dispersion prepared in
1. above 6.0 parts (Silica sol) Colloidal silica (average particle
size 120 nm) 2.0 parts Methyl ethyl ketone 1.4 parts (Other
components) Stearic acid 2.0 parts Amide stearate 0.2 part.sup.
Butyl stearate 2.0 parts Polyisocyanate 2.5 parts (Coronate
(Japanese registered trademark) made by Nippon Polyurethane
Industry Co., Ltd. (Finishing solvents) Cyclohexanone 200.0 parts
Methyl ethyl ketone 200.0 parts
In Table 5, BF denotes ferromagnetic barium ferrite powder with an
average particle size (average plate diameter) of 21 nm and MP
denotes ferromagnetic metal powder with an average particle size
(average major axis length) of 30 nm.
3. Formula of Nonmagnetic Layer Forming Composition
TABLE-US-00002 Nonmagnetic inorganic powder: .alpha.-iron oxide
100.0 parts Average particle size (average major axis length): 0.15
.mu.m Average acicular ratio: 7 BET specific surface area: 52
m.sup.2/g Carbon black 20.0 parts Average particle size: 20 nm
Polyurethane resin containing SO.sub.3Na groups 18.0 parts Weight
average molecular weight: 70,000 SO.sub.3Na groups: 0.2 meq/g
Stearic acid See Table 5 Amide stearate See Table 5 Butyl stearate
See Table 5 Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0
parts
4. Formula of Backcoat Layer Forming Composition
TABLE-US-00003 Nonmagnetic inorganic powder: .alpha.-iron oxide
80.0 parts Average particle size (average major axis length): 0.15
.mu.m Average acicular ratio: 7 BET specific surface area: 52
m.sup.2/g Carbon black 20.0 parts Average particle size 20 nm Vinyl
chloride copolymer 13.0 parts Polyurethane resin containing
sulfonate groups 6.0 parts Phenylphosphonic acid 3.0 parts
Cyclohexanone 155.0 parts Methyl ethyl ketone 155.0 parts
Polyisocyanate 5.0 parts Cyclohexanone 200.0 parts
5. Preparation of Various Layer Forming Compositions
The magnetic layer forming composition was prepared by the
following method. The above magnetic liquid was prepared using a
batch-type vertical sand mill to disperse (bead dispersion) the
various components for 24 hours. Zirconia beads of 0.5 mm .phi.
were employed as the dispersion beads. Using the above sand mill,
the magnetic liquid that had been prepared and the above abrasive
liquid were mixed with the other components (silica sol, other
components, and finishing solvents) and dispersed with beads for 5
minutes. Subsequently, a batch-type ultrasonic device (20 kHz, 300
W) was used to conduct processing for 0.5 minutes (ultrasonic
dispersion). Subsequently, filtration was conducted with a filter
having an average pore size of 0.5 .mu.m to prepare the magnetic
layer forming composition.
The nonmagnetic layer forming composition was prepared by the
following method. The various components excluding the stearic
acid, cyclohexanone, and methyl ethyl ketone were dispersed for 24
hours in a batch-type vertical sand mill to obtain a dispersion.
Zirconia beads of 0.5 mm .phi. were employed as the dispersion
beads. Subsequently, the remaining components were added to the
dispersion that had been obtained, and stirring was conducted in a
dissolver. The dispersion thus obtained was filtered with a filter
having an average pore size of 0.5 .mu.m to prepare the nonmagnetic
layer forming composition.
The backcoat layer forming composition was prepared by the
following method. The various components excluding the
polyisocyanate and cyclohexanone were kneaded and diluted in an
open kneader. Subsequently, a horizontal-type bead mill disperser
was used to conduct dispersion with 1 mm .phi. zirconia beads at a
bead fill rate of 80% and a rotor tip speed of 10 m/s in 12 passes
with a residence time of 2 minutes per pass. Subsequently, the
remaining components were added to the dispersion that had been
obtained and stirring was conducted in a dissolver. The dispersion
thus obtained was filtered with a filter having an average pore
diameter of 1 .mu.m to prepare the backcoat layer forming
composition.
6. Fabrication of Magnetic Tape
A magnetic tape was fabricated by the specific embodiment shown in
FIG. 1. Specifically, this was done as follows.
A support made of polyethylene naphthalate 4.50 .mu.m in thickness
was fed out from a feeding part. In a first coating part, the
nonmagnetic layer forming composition prepared in 5. above was
coated on one surface in a first coating part so as to yield the
dry thickness shown in Table 5 upon drying to form a coating layer.
While the coating layer that had been formed was still wet, it was
passed through a cooling zone that had been adjusted to an
atmospheric temperature of 0.degree. C. with the residence time
indicated in Table 5 to conduct a cooling step. Subsequently, it
was passed through a first heat treatment zone with an atmospheric
temperature of 100.degree. C. to conduct a heating and drying step,
thus forming a nonmagnetic layer.
Subsequently, the magnetic layer forming composition prepared in 5.
above was coated over the nonmagnetic layer so as to yield a
thickness upon drying of 60 nm in a second coating part to form a
coating layer. While this coating layer was still wet (had not yet
dried), a magnetic field with a magnetic strength of 0.3 T was
applied perpendicularly with respect to the surface of the coating
layer of the magnetic layer forming composition in an orienting
zone to conduct a perpendicular orientation processing.
Subsequently, drying was conducted in a second heat treatment zone
(with an atmospheric temperature of 100.degree. C.).
Subsequently, the backcoat layer forming composition prepared in 5.
above was coated in the third coating part so as to yield a
thickness upon drying of 0.60 .mu.m on the opposite surface of the
polyethylene naphthalate support from the surface on which the
nonmagnetic layer and magnetic layer had been formed, forming a
coating layer. The coating layer that had been formed was dried in
a third heat treatment zone (with an atmospheric temperature of
100.degree. C.).
Subsequently, a calendering processing (surface smoothing
treatment) was conducted with a calender comprised solely of metal
rolls at a speed of 80 m/minute, a linear pressure of 300 kg/cm,
and a temperature of 100.degree. C. A 36 hour heat treatment was
then conducted in an environment of an atmospheric temperature of
70.degree. C. Following the heat treatment, the product was slit to
a width of 1/2 inch (0.0127 meter) to obtain a magnetic tape.
In Comparative Examples 1 to 19 for which "Not implemented" is
recorded in the cooling zone residence time column in Table 5,
magnetic tapes were fabricated by a manufacturing process that did
not include a cooling zone.
In Comparative Example 19, following the above calendering
processing, a corona treatment was implemented on the surface of
the magnetic layer by the method given below, followed by the
application of a stearic acid overcoat.
A corona treatment was implemented by the method described in
Japanese Unexamined Patent Publication (KOKAI) No. 2008-243317,
paragraph 0138, on the surface of the magnetic layer. Next, a 10%
methyl ethyl ketone solution of stearic acid was applied with a
wire bar and dried on the surface of the magnetic layer that had
been subjected to the corona treatment, after which the above heat
treatment and slitting were conducted.
The thickness of the various layers of the magnetic tapes that had
been fabricated and the nonmagnetic support was determined by the
following method. The thickness of the various layers that had been
formed was confirmed to be the thickness indicated in Table 5
above.
The cross section of the magnetic tapes in the direction of
thickness was exposed by ion beam, and observation of the exposed
cross section was conducted by a scanning electron microscope. In
observing the cross section, the various thicknesses were obtained
as the arithmetic average of thicknesses obtained in two spots in
the direction of thickness.
[Evaluation Methods]
1. Magnetic Layer Side Surface Extraction Quantity
The backcoat layer of each of the magnetic tapes fabricated was
removed by rubbing it against a piece of filter paper impregnated
with tetrahydrofuran (THF). The removal operation was conducted
until no black material derived from the backcoat layer came off on
filter paper. A tape sample was then obtained by cutting 5 cm in
the longitudinal direction.
The tape sample obtained was placed in a beaker, into which 30 mL
of methanol was poured and a lid was applied.
The tape sample was immersed in methanol, heated to a solution
temperature of 60.degree. C., and subjected to an extraction
operation for 3 hours.
The liquid following extraction was transferred to an
eggplant-shaped flask and the methanol was evaporated using a
rotary evaporator.
Subsequently, 1 mL of a 1:1 (by volume) mixed solution of methanol
and chloroform was added with a pipette to dissolve the extract
anew. A 50 .mu.L quantity of a methylating agent (tetramethyl
ethylene diamine (TMSDA)) was admixed with a microsyringe and the
mixture was reacted for 30 minutes at room temperature to obtain a
sample for gas chromatography measurement.
Subsequently, a gas chromatography method was employed under the
following measurement conditions to detect a fatty acid, fatty acid
ester, and fatty acid amide. A calibration curve that had been
prepared in advance was then used for quantification. The various
extraction quantities of stearic acid, amide stearate, and butyl
stearate per unit area of magnetic tape were obtained from the
measurement values, after which the stearic acid extraction
quantity and the amide stearate extraction quantity were added to
calculate the magnetic layer side surface extraction quantity.
(Measurement Conditions) Device: Agilent 7890A (FID detector)
Column: Agilent J&W DB-1HT Oven temperature: 150.degree. C./2
minutes.fwdarw.10.degree. C./1 minute, raised to 300.degree. C.
Inlet temperature: 310.degree. C., pulsed splitless injection
Injection quantity: 1 .mu.L, Detector: FID (flame ionization
detector) (340.degree. C.) Carrier gas: He
2. C Concentration (10 degrees), C Concentration (90 degrees)
X-ray photoelectron spectroscopy was conducted with an ESCA device
on the magnetic layer side surface (measurement region: 300
.mu.m.times.700 .mu.m) of the magnetic tapes of Examples and
Comparative Examples by the following method. The C concentration
(10 degrees) and the C concentration (90 degrees) were calculated
from the analysis results. The calculated values are given in Table
5.
(Analytic and Calculation Methods)
The measurements of (1) to (3) below were all conducted under the
conditions shown in Table 1.
TABLE-US-00004 TABLE 1 Device AXIS-ULTRA made by Shimadzu Corp.
Excitation X-ray source Monochromatized Al-K.alpha. radiation
(output: 15 kV, 20 mA) Analyzer mode Spectrum Lens mode Hybrid
(analysis area: 300 .mu.m .times. 700 .mu.m) Neutralizing electron
gun for charge On (used) compensation (charge neutralizer)
Photoelectron take-off angle 10 deg. or 90 deg. (angle of device
relative to sample surface)
(1) Wide Scan Measurement
The types of elements detected by wide scan measurement
(measurement conditions: see Table 2) by ESCA on the magnetic layer
side surface of the magnetic tape were examined (qualitative
analysis).
TABLE-US-00005 TABLE 2 Energy Cumulative resolution Pickup time
number Scan range Pass energy (step) (Dwell) (Sweeps) 0 to 1200 eV
160 eV 1 eV/step 100 ms/step 5
(2) Narrow Scan Measurement
Narrow scan measurement (measurement conditions: see Table 3) was
conducted for each of the elements detected in (1) above. The
auxiliary data processing software of the device (Vision 2.2.6) was
employed to calculate the atomic concentration (unit: atom %) of
each element detected in the peak areas of the various elements.
The C concentration was also calculated from the peak area of the
C1s spectrum.
TABLE-US-00006 TABLE 3 Energy Cumulative resolution Pickup time
number Spectrum.sup.Note 1) Scan range Pass energy (Step) (Dwell)
(Sweeps).sup.Note 2) C1s 276 to 296 eV 80 eV 0.1 eV/step 100
ms/step 3 Cl2p 190 to 212 eV 80 eV 0.1 eV/step 100 ms/step 5 N1s
390 to 410 eV 80 eV 0.1 eV/step 100 ms/step 5 O1s 521 to 541 eV 80
eV 0.1 eV/step 100 ms/step 3 Fe2p 700 to 740 eV 80 eV 0.1 eV/step
100 ms/step 3 Ba3d 765 to 815 eV 80 eV 0.1 eV/step 100 ms/step 3
Al2p 64 to 84 eV 80 eV 0.1 eV/step 100 ms/step 5 Y3d 148 to 168 eV
80 eV 0.1 eV/step 100 ms/step 3 P2p 120 to 140 eV 80 eV 0.1 eV/step
100 ms/step 5 Zr3d 171 to 191 eV 80 eV 0.1 eV/step 100 ms/step 5
Bi4f 151 to 171 eV 80 eV 0.1 eV/step 100 ms/step 3 Sn3d 477 to 502
eV 80 eV 0.1 eV/step 100 ms/step 5 Si2p 90 to 110 eV 80 eV 0.1
eV/step 100 ms/step 5 S2p 153 to 173 eV 80 eV 0.1 eV/step 100
ms/step 5 .sup.Note 1)The spectrum (type pf element) shown in Table
3 is an example. When an element that is not shown in Table 3 was
detected in the qualitative analysis of (1), identical narrow scan
measurements were conducted over a scan range containing all of the
spectra of elements detected. .sup.Note 2)For spectra with good
signal-to-noise (S/N) ratios, measurements were taken a total of
three times. However, the quantitative results were not affected
for any of the spectra when measurements were taken a total of five
times.
The arithmetic average of values obtained by conducting the above
processing three times at different spots on the magnetic layer
side surface of the magnetic tape were adopted for the C
concentration (10 degrees) and C concentration (90 degrees). The
calculated values are given in Table 5.
(3) Obtaining the C1s Spectrum
C1s spectra were obtained under the measurement conditions given in
Table 4 to determine the contribution of the fatty acid and the
fatty acid amide to the C concentration (10 degrees), described
further below, in the magnetic tape of Example 1. The auxiliary
data processing software (Vision 2.2.6) of the device was used to
compensate for the shift (physical shift) due to the sample charge
in the C1s spectrum obtained. The same software was then used to
conduct fitting (peak separation) of the C1s spectrum. In peak
separation, a Gauss--Lorentz complex function (Gauss component 70%,
Lorentz component 30%) was employed, fitting of the C1s spectrum
was conducted by the nonlinear least squares method, and the
proportion of the C--H peak accounted for by the C1s spectrum (peak
area ratio) was calculated. The calculated C--H peak area ratio was
multiplied by the C concentration obtained in (2) above to
calculate the C--H derived C concentration. The term "C--H derived
C concentration" is the proportion accounted for by carbon atoms C
constituting the C--H bond relative to the total (based on atoms)
100 atom % of all elements detected by qualitative analysis by
ESCA. In the X-ray photoelectron spectra (X-axis: bond energy,
Y-axis: intensity) obtained by ESCA analysis, the C1s spectrum
contains information relating to the energy peak of the is orbital
of carbon atoms C. In this C is spectrum, the peak positioned near
a bond energy of 284.6 eV is the C--H peak. This C--H peak is
derived from the bond energy of the C--H bond of organic
compounds.
TABLE-US-00007 TABLE 4 Energy Cumulative Scan Pass resolution
Pickup time number Spectrum range energy (Step) (Dwell) (Sweeps)
C1s 276 to 10 eV 0.1 eV/step 200 ms/step 20 296 eV
3. Determination of Contribution of Fatty Acid and Fatty Acid Amide
to C Concentration (10 Degrees)
(1) Two magnetic tapes (sample tapes) were fabricated by the same
method as in Example 1. One of the sample tapes was measured with
the above ESCA device and the other sample tape was not, after
which solvent extraction was conducted (solvent: methanol).
When gas chromatographic analysis was used to quantify the fatty
acid, fatty acid amide, and fatty acid ester in the solutions
obtained by extraction, almost no difference in quantitative values
were observed for fatty acid (stearic acid) and fatty acid amide
(amide stearate) in the two sample tapes. However, for fatty acid
ester (butyl stearate), the quantitative value in the sample tape
following measurement was much lower than the quantitative value in
the unmeasured sample tape. This was attributed to the fatty acid
ester having volatized in the vacuum chamber in which the sample
being measured was placed during measurement in the ESCA
device.
Based on these results, the C concentration (10 degrees) obtained
by ESCA analysis was determined not to be affected by the fatty
acid ester. Similarly, it was determined that the fatty acid ester
did not affect the C concentration (90 degrees).
(2) Components contained in the magnetic layer forming composition
and components that are contained in the nonmagnetic layer forming
composition and may migrate from the nonmagnetic layer to the
magnetic layer in a magnetic tape and can thus be present in the
magnetic layer are organic compounds excluding solvents and
polyisocyanate (being crosslinked by heating in the heat treatment
and/or calendaring processing) in the form of stearic acid, amide
stearate, butyl stearate, 2,3-dihydroxynaphthalene, and
polyurethane resin. Of these components, butyl stearate, as stated
above, has been determined not to affect the C concentration (10
degrees) based on the results of (1) above.
The effects of 2,3-dihydroxynaphthalene and polyurethane resin on
the C concentration (10 degrees) were determined by the following
method.
For the 2,3-dihydroxynaphthalene and polyurethane resin employed in
Example 1, C1s spectra were obtained at a photoelectron take-out
angle of 10 degrees by the same method as above. In the spectra
obtained, the peak located near a bond energy of 286 eV and the
C--H peak were separated by the processing set forth above. The
proportion (peak area ratio) of the C1s spectrum accounted for by
the various separated peaks was calculated and the peak area ratio
of the peak located near a bond energy of 286 eV and the C--H peak
was calculated.
Next, in the C1s spectrum obtained at a photoelectron take-out
angle of 10 degrees in Example 1, the peak positioned near the bond
energy of 286 eV was separated by the processing set forth above.
Although 2,3-dihydroxynaphthalene and polyurethane resin have peaks
located near the bond energy of 286 eV in the C1s spectrum, the
fatty acid (stearic acid) and the fatty acid amide (amide stearate)
do not have peaks at that location. Accordingly, the peaks
positioned near the bond energy of 286 eV in the C1s spectrum
obtained at a photoelectron take-out angle of 10 degrees in Example
1 were determined to be derived from 2,3-dihydroxynaphthalene and
polyurethane resin. Accordingly, using these peaks, the
contribution of 2,3-dihydroxynaphthalene and polyurethane resin to
the C concentration (10 degrees) obtained in Example 1 was
calculated to be less than or equal to 20%. Based on these results,
much of the C concentration (10 degrees) was determined to have
been derived from the fatty acid (stearic acid) and the fatty acid
amides (amide stearate).
Based on the above results, the C concentration (10 degrees) was
demonstrated to be an indicator of the amount of fatty acid and
fatty acid amide present. When the same determinations were made
for the C concentration (90 degrees), most of the C concentration
(90 degrees) was similarly determined to have been derived from the
fatty acid (stearic acid) and the fatty acid amide (amide
stearate).
4. Dropout
Dropout was measured with a 1/2 inch (0.0127 meter) reel tester to
which a head had been secured. A writing head was used to write a
signal at a recording wavelength of 250 kfci. This was reproduced
with a giant magnetoresistive (GMR) head with a track width of 1
.mu.m. The number of signal dropouts of 0.4 .mu.m or more in length
at an output drop of greater than or equal to 40% relative to the
average output was detected and the number per 1 m of tape length
(per measurement area 1 mm.sup.2 (=track width (1 .mu.m).times.tape
length (1 m)) was adopted as the dropout. From the perspective of
lowering the error rate, a dropout of less than or equal to
900/mm.sup.2 is desirable.
5. Resistance to Scratching
The resistance to scratching of the magnetic tapes was evaluated
with a measurement apparatus in the form of a Triboster TS501 made
by Kyowa Interface Science. The magnetic tape was secured to the
stage of the measurement device in an environment of 23.degree. C.
and 50% relative humidity, a point contacter in the form of a 3 mm
.phi. steel ball was pressed down with a load of 10 g, and the
point contacter was passed 300 times across the surface on the
magnetic layer side over a slide length of 10 mm at a speed of 3
mm/s. The surface on the magnetic layer side of the magnetic tape
following sliding was observed at 50.times. magnification with a
light interference microscope and the presence of scratching was
evaluated. A: No or slight scratching observed B: Scratching
observed (more severe than A). C: Scratching observed (more severe
than B). D: Scratching observed (more severe than C).
6. Centerline Average Surface Roughness Ra Measured with a
Noncontact Surface Profiler on the Magnetic Layer Side Surface
The centerline average surface roughness Ra was measured on the
surface on the magnetic layer side by the method set forth above
with a noncontact optical roughness profiler in the form of a
Newview 5022 made by Zygo. The measurement results are given in
Table 5.
TABLE-US-00008 TABLE 5 Unit Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex.
7 Magnetic layer Ferromagnetic powder BF BF BF BF BF BF BF
Nonmagnetic layer thickness .mu.m 0.40 0.40 0.40 0.20 0.20 0.10
0.10 Nonmagnetic layer forming Stearic acid content part 2.0 2.0
2.0 2.0 2.0 2.0 2.0 composition Amide stearate content part 0.2 0.2
0.2 0.2 0.2 0.2 0.2 Butyl stearate content part 2.0 2.0 2.0 2.0 2.0
2.0 2.0 Residence time in cooling 1 sec. 5 sec. 10 sec. 1 sec. 5
sec. 5 sec. 10 sec. zone Lubricant extraction quantity {circle
around (1)} Stearic acid mg/m.sup.2 13.1 13.0 13.0 12.0 11.6 10.0
10.1 {circle around (2)} Amide stearate mg/m.sup.2 1.6 1.6 1.6 1.4
1.4 1.2 1.2 {circle around (3)} Butyl stearat mg/m.sup.2 13.5 13.6
13.6 9.5 9.3 6.2 6.0 {circle around (1)} + {circle around (2)}
(Stearic acid + mg/m.sup.2 14.7 14.6 14.6 13.4 13.0 11.2 11.3 Amide
stearate) C concentration C concentration (10 degrees) atom % 54 68
78 51 65 52 62 C concentration (90 degrees) atom % 49 48 48 42 42
36 38 Centerline average surface roughness Ra nm 1.5 1.7 1.8 1.6
1.7 1.5 1.5 Dropout /mm.sup.2 810 800 800 580 620 500 480
Resistance to scratching A A A A A A A Ex. 8 Ex. 9 Ex. 10 Ex. 11
Ex. 12 Ex. 13 Ex. 14 Magnetic layer Ferromagnetic powder BF BF BF
BF BF MP BF Nonmagnetic layer thickness 0.10 0.05 0.05 0.40 0.20
0.10 0.40 Nonmagnetic layer forming Stearic acid content 2.0 2.0
2.0 2.0 2.0 2.0 2.0 composition Amide stearate content 0.2 0.2 0.2
0.2 0.2 0.2 0.2 Butyl stearate content 2.0 2.0 2.0 4.0 8.0 2.0 4.0
Residence time in cooling zone 50 sec. 5 sec. 50 sec. 5 sec. 5 sec.
10 sec. 300 sec. Lubricant extraction quantity {circle around (1)}
Stearic acid 10.0 8.6 8.6 13.1 11.8 9.8 13.0 {circle around (2)}
Amide stearate 1.2 0.4 0.4 1.5 1.3 1.2 1.5 {circle around (3)}
Butyl stearat 6.0 4.5 4.5 18.2 18.0 5.9 18.0 {circle around (1)} +
{circle around (2)} (Stearic acid + 11.2 9.0 9.0 14.6 13.1 11.0
14.5 Amide stearate) C concentration C concentration (10 degrees)
80 50 78 69 66 55 83 C concentration (90 degrees) 37 32 31 48 43 37
48 Centerline average surface roughness Ra 1.8 1.5 1.8 1.6 1.6 1.6
2.3 Dropout 490 390 400 810 610 420 800 Resistance to scratching A
A A A A A A Comp. Comp. Comp. Comp. Comp. Comp. Comp. Unit Ex. 1
Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Magnetic layer Ferromagnetic
powder BF BF BF BF BF BF BF Nonmagnetic layer thickness .mu.m 1.00
0.80 0.60 0.60 0.50 0.50 0.40 Nonmagnetic layer forming Stearic
acid content part 2.0 2.0 2.0 3.3 2.0 3.2 2.0 composition Amide
stearate content part 0.2 0.2 0.2 0.3 0.2 0.3 0.2 Butyl stearate
content part 2.0 2.0 2.0 3.3 2.0 3.2 2.0 Residence time in cooling
Not Not Not Not Not Not Not zone imple- imple- imple- imple- imple-
imple- imple- mented mented mented mented mented mented mented
Lubricant extraction quantity {circle around (1)} Stearic acid
mg/m.sup.2 22.0 19.2 15.9 21.5 14.3 19.0 13.2 {circle around (2)}
Amide stearate mg/m.sup.2 2.6 2.3 1.9 2.6 1.7 2.2 1.6 {circle
around (3)} Butyl stearat mg/m.sup.2 20.0 18.2 15.8 20.4 14.2 18
13.4 {circle around (1)} + {circle around (2)} (Stearic acid +
mg/m.sup.2 24.6 21.5 17.8 24.1 16.0 21.2 14.8 Amide stearate) C
concentration C concentration (10 degrees) atom % 60 55 42 54 38 43
36 C concentration (90 degrees) atom % 65 61 57 62 53 60 48
Centerline average surface roughness Ra nm 1.8 1.8 1.7 1.8 1.5 1.5
1.7 Dropout /mm.sup.2 1250 1180 1080 1280 1010 1100 800 Resistance
to scratching A A B A B B C Comp. Comp. Comp. Comp. Comp. Comp.
Comp. Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Magnetic layer
Ferromagnetic powder BF BF BF BF BF BF BF Nonmagnetic layer
thickness 0.40 0.40 0.20 0.20 0.20 0.10 0.10 Nonmagnetic layer
forming Stearic acid content 4.0 2.0 2.0 8.0 2.0 2.0 16.0
composition Amide stearate content 0.4 0.2 0.2 0.8 0.2 0.2 1.6
Butyl stearate content 4.0 4.0 2.0 8.0 8.0 2.0 16.0 Residence time
in cooling zone Not Not Not Not Not Not Not imple- imple- imple-
imple- imple- imple- imple- mented mented mented mented mented
mented mented Lubricant extraction quantity {circle around (1)}
Stearic acid 17.8 13.1 11.9 18.0 11.8 10.2 17.6 {circle around (2)}
Amide stearate 2.1 1.6 1.4 2.2 1.4 1.2 2.1 {circle around (3)}
Butyl stearat 18.3 18.4 9.5 18.2 17.8 6.0 17.9 {circle around (1)}
+ {circle around (2)} (Stearic acid + 19.9 14.7 13.3 20.2 13.2 11.4
19.7 Amide stearate) C concentration C concentration (10 degrees)
48 35 34 46 35 29 46 C concentration (90 degrees) 60 49 42 58 42 37
54 Centerline average surface roughness Ra 1.6 1.6 1.5 1.6 1.5 1.5
1.6 Dropout 1150 810 600 1130 610 500 1110 Resistance to scratching
B C C B C D B Comp. Comp. Comp. Comp. Comp. Ex. 15 Ex. 16 Ex. 17
Ex. 18 Ex.19 Magnetic layer Ferromagnetic powder BF BF MP MP BF
Nonmagnetic layer thickness 0.10 0.05 0.10 0.10 0.10 Nonmagnetic
layer forming Stearic acid content 20.0 2.0 2.0 16.0 2.0
composition Amide stearate content 2.0 0.2 0.2 1.6 0.2 Butyl
stearate content 20.0 2.0 2.0 16.0 2.0 Residence time in cooling
zone Not Not Not Not Not implemented implemented implemented
implemented implemented Lubricant extraction quantity {circle
around (1)} Stearic acid 20.8 8.6 10.1 18.5 22.0 {circle around
(2)} Amide stearate 2.5 0.4 1.2 2.2 1.2 {circle around (3)} Butyl
stearat 20.1 4.5 6.2 18.2 6.0 {circle around (1)} + {circle around
(2)} (Stearic acid + 23.3 9.0 11.3 20.7 23.2 Amide stearate) C
concentration C concentration (10 degrees) 54 26 36 48 32 C
concentration (90 degrees) 62 34 39 54 66 Centerline average
surface roughness Ra 1.5 1.5 1.7 1.6 1.5 Dropout 1240 400 500 1120
1200 Resistance to scratching A D C B D *Stearic acid overcoat
Based on the results given in Table 5, the magnetic tapes of
Examples were confirmed to have achieved improved resistance to
scratching and reduced dropout.
An aspect of the present invention is useful in the field of
manufacturing magnetic tapes such as backup tapes.
Although the present invention has been described in considerable
detail with regard to certain versions thereof, other versions are
possible, and alterations, permutations and equivalents of the
version shown will become apparent to those skilled in the art upon
a reading of the specification. Also, the various features of the
versions herein can be combined in various ways to provide
additional versions of the present invention. Furthermore, certain
terminology has been used for the purposes of descriptive clarity,
and not to limit the present invention. Therefore, any appended
claims should not be limited to the description of the preferred
versions contained herein and should include all such alterations,
permutations, and equivalents as fall within the true spirit and
scope of the present invention.
Having now fully described this invention, it will be understood to
those of ordinary skill in the art that the methods of the present
invention can be carried out with a wide and equivalent range of
conditions, formulations, and other parameters without departing
from the scope of the invention or any Examples thereof.
All patents and publications cited herein are hereby fully
incorporated by reference in their entirety. The citation of any
publication is for its disclosure prior to the filing date and
should not be construed as an admission that such publication is
prior art or that the present invention is not entitled to antedate
such publication by virtue of prior invention.
* * * * *